Radiant energy transmission system



March 8, 1955 G. WILKES RADIANT ENERGY TRANSMISSION SYSTEM 2Sheets-Sheet 1 Filed Jan. 9, 1946 Oscillator March 8, 1955 s. WILKES2,703,882

RADIANT ENERGY TRANSMISSION SYSTEM Filed Jan. 9, 1946 2 Sheets-Sheet 2INVENTOR GILBE 7' WILKES HEATER 4-10 v AC 6 4 Vill? RADIANT ENERGYTRANSMISSION SYSTEM Gilbert Wilkes, Washington, D. C., assignor to theUnited States of America as represented by the Secretary of the NavyApplication January 9, 1946, Serial No. 640,110

19 Claims. (Cl. 343100) The present invention relates to apparatus andprocesses concerning radiant-energy transmission systems. Itcontemplates the provision of an artificial electron cloud forreflecting high frequency electromagnetic waves. It also embraces theprovision of such an electron cloud for guiding or confining aradiant-energy beam along a predetermined pathof travel or within achamber. In its broad aspect the invention comprises means and processesfor artificially providing an electron cloud and for so controlling thatcloud as to attenuate, guide, reflect, confine or otherwise directelectromagnetic wave energy.

The cloud may be used as a wave guide, as an attenuator, as a confiningportion of a wave guide, as a choke or as a reflector. Since such acloud may be deflected by the application of suitable magnetic orelectrostatic potentials, this invention in a more narrow aspectcomprises means and processes for artificially providing an electroncloud whereby to direct a high-frequency electromagnetic wave, and fordeflecting that cloud, whereby the direction of travel of the wave isvaried. Since the cloud is substantially inertialess, this inventionprovides a means and method for changing the direction of travel ofelectromagnetic wave energy, which means and method do not sufler fromthe disadvantages attendant upon the use of mechanical systems.

While this invention has a wide range of prospective application. it isof particular utility as embodied in a nutator. The development of anutator free from the limitations inherent in the inertia, friction andelastance parameters of mechanical systems posed the problem solved bythis invention. The invention is herein described, by way ofillustration and not of limitation, as incorporated in a nutator. itwill be understood by those skilled in the fire-control radar art that anutator is a device employed in radio direction and ranging systems forsearching and scanning a target. Prior-art nutators have been premisedon mechanisms for angularly so moving an antenna assembly or otherradiating expedient that the axis of a beam of electromagnetic energy(hereinafter referred to as the radar beam) generates a cone of circularor elliptic section. The position of the target is precisely ascertainedby means of associated signal circuits which respond to the behavior ofthe echo signals as the radar beam is nutated.

The above-mentioned mechanical nutators are subject to the followingmajor disadvantages: (l) the rapidity of their action is limited bytheir inertia; (2) they require complex arrangements of gears, shafts,eccentrics and the like for moving the radiating member; and (3) theyalso involve complicated means for preventing transmission losses ofelectromagnetic energy, discontinuities.

and resultant undesired wave reflections.

it is an object of this invention to prov de a novel electrical devicefor confining electromagnetic wave energy- Another object of thisinvention IS to provide a novel device for attenuating wave energy.

It is also an object of this invention to provide a novel electricaldevice for reflecting electromagnetic wave energy.

A further object of this invention is to provide a novel electricaldevice for guiding electromagnetic wave energy.

Another object of this invention is to provide a substantiallyinertialess device for changing the direction of propagation orreception of electromagnetic wave energy.

2,703,882 Patented Mar. 8, 1955 A primary object of this invention is toprovide an electronic device for controlling the direction ofpropagation of radiant energy.

A secondary object of this invention, as embodied in a nutator,comprises the providing of a novel wave guide having such operation thatit rapidly responds to control signals to change the direction oftransmission of electromagnetic wave energy.

Such objects also include the providing of a nutator having no movingparts.

Another object of this invention is to provide an improved electronictube for controlling a characteristic of an electromagnetic wave beam.

Among the objects of this invention is the providing of a novelcombination of a tube for controlling a characteristic of a radar beamor the like and a conventional wave guide for introducing the beam intothe tube.

Other objects are the providing of processes for accomplishing theabove-mentioned objectives and of means for avoiding the disadvantagesand limitations of priorart nutators.

For an understanding of the present invention together with other andfurther objects thereof reference is made to the followingspecification, to the claims appended thereto, and to the accompanyingdrawings in which:

Figure 1 illustrates a radiant-energy transmission system in accordancewith this invention, a conventional high-frequency electromagneticenergy source being shown in block form and this improved nutatingdevice being shown in section;

Figure 2 is a perspective view, partly broken away, of this improvednutator, showing in detail the electron gun structure thereof; and

Figures 3, 4 and 5 are sectional views of the nutator taken on theplanes indicated by the lines 3--3, and 55, respectively, of Fig. 1,looking in the direction of the arrows.

Referring now specifically to Fig. 1 there is illustrated in block forman oscillator 10, which may be a conventional source of high frequencyelectromagnetic energy. The numeral 11 represents an evacuated envelopehaving an end portion 12 which is transparent to and readily passeselectromagnetic wave energy of the frequency employed in radar beams.

A suitable base 13 is provided for carrying the terminals of the tubeelectrodes. Centrally located in this base is an opening for a waveguide 14, here shown as circular in cross-section. This tubular metallicwave guide 14 is sealed vacuum-tightly into the envelope 11 at the placewhere it enters the latter. The tube is closed by a partition 15, whichforms a tight joint with the wall of the wave guide 14. This partitionis made of non-conducting material, to minimize obstruction of theenergy entering the tube envelope 11 through the wave guide 14. Thisenergy would be short-circuited or reflected in an undesirable manner ifthe partition 15 were made of conductive material. The positions andthicknesses of the partition 15 and of the end wall 12 are so determinedas to eliminate any undesired reflection which might otherwise be set upbetween them. The wave guide 14 is coupled to the radio frequency energysource 10 by any suitable conventional expedient.

A flat, ring-shaped cathode 18, of the indirectly heated type, ismounted radially outwardly from and coaxially with that portion of thewave guide 14 which projects within envelope 11. The cathode 18 ismounted on a suitable support 31, as shown in Fig. 2. The cathode 18 isgrounded as indicated at 53. A cathode heater element 32 is wound on asuitable circular supporting form 33 and the latter is secured to thetube base by any suitable mounting expedient 34. Conductors 35 and 36connect the heater to any suitable power source (4-10 volts, alternatingcurrent). Also disposed radially outwardly from and coaxially with thewave guide 14 is a focusing grid 37 suitably mounted on a support 38.The grid 37 comprises two flanged portions, one located radiallyinwardly from cathode 18 and the other located radially outwardly fromthe cathode. The grid 37 is negatively charged in order to compress theelectron flow as desired. The grid 37 is connected to the negativeterminal of a suitable source of biasing potential (0-100 volts) byconductor 39 and the positive terminal of this source is grounded. Theelectron gun structure is completed by an accelerating anode 40, whichhas flange portions located radially inwardly and outwardly of cathodel8 and is mounted on an appropriate support 54. The accelerating anode40 is connected to the terminal of a suitable source of space current(100 -500 volts, positive with respect to cathode) by conductor 55. Thiselectron gun structure diflers from the conventional electron gunprimarily in the respect that it produces a stream of electrons in theform of a tube rather than in the form of a beam or pencil. For thepurpose of defleeting this stream there are provided a set of left-rightdeflecting plates 41-42 and a set of up-down deflecting plates 43-44. Asbest seen in Fig. 3, each of these plates is bent into an arc to the endthat the circular shape of the electron stream may be maintained. Thesets of plates are in space quadrature. Time-quadrature voltages areproduced individually in the inductances 45, 46 by a suitablealternating current source. One of these quadrature beam-deflectingvoltages is applied to plates 41-42 by conductors 47, 48. The other ofthese deflecting voltages is applied to plates 43-44 by conductors 49,50. In order to vary the beam deflecting potentials, sliders 51, 56 areprovided. For the purpose of controlling the desired flaring of theelectron cloud or horn 29, a positive potential is applied to all of theplates 41-44 by a suitable direct current source (not shown) through anetwork comprising conductor 57 and resistors 58 and 59, resistor 58being connected across conductors 47, 48, resistor 59 being connectedacross conductors 49, 50 and conductor 57 being connected to center tapson resistors 58, 59. When all of the plates are made more positive, theelectron horn is made more divergent.

A conductive coating 61 is provided on the interior surface of theenvelope 11 to act as a collector electrode and to afford a return pathto the cathode circuit for the cathode-ray beam current. This coatingmay be of a conventional type consisting of a layer of graphite appliedto the inside surface of the glass.

The degree of evacuation of the envelope is important. To reflect a waveof a definite frequency a definite electronic concentration is necessaryat which transmission by penetration of the wave through the electroncloud is nil and reflection is lossless. To reflect a wave of a definitepower, a definite depth of electron cloud is necessary, below whichpartial transmission (i. e., penetration of the wave through theelectron cloud) will occur. The walls of the electronic wave guide 29must therefore have at least a minimum concentration and thickness inorder to handle a given wave of electromagnetic energy, whichrequirement results in relatively high cathodic current for the usualradar beams unless the bulk of this concentration is obtained bysecondary ionization. On the other hand, high power energy waves willspontaneously ionize the gas in a poor vacuum such as is used in neonilluminating tubes and will cause cut off of said energy. A vacuum isprovided such that the residual gas pressure lies between lmm. and 2x10-mm. of mercury.

Such an atmosphere is found in the usual cathode-ray tube. It will notionize spontaneously when subjected to high power waves. When properpotentials are applied to the cathode and to the control grid 37, thetube produces a cathode-ray beam consisting of emitted electrons plusthe positive ions generated thereby. This beam is tubular and it acts asa wave guide extension for energy propagated through the wave guide 14in the direction indicated by the large arrow. The cathode ray beam 29serves as an extension of the wave guide 14. This extension or hornformed by the cloud 29 has several interesting properties. First, it isa flexible extension because it can be deflected by the application ofsuitable potentials to the deflecting plates 4l-44, which potentials areapplied in a manner well known to those skilled in the cathode ray tubeart. For example, if equal alternating current voltages in timequadrature are ap' plied to the deflecting elements 41--42, 43-44. theaxis of the cathode ray tube beam will describe a constructive circulartrace on the end 12 of the envelope. If one of the two deflectingpotentials is of higher magnitude than the other, an elliptic trace willresult, and so on. These facts provide the proper basis for nutation.The reason for this is that as the beam 29, which acts as a wave guideextension, is nutated, so too the radiant energy beam which passesthrough the wave guide and extension is nutated.

Additionally, by varying the electronic concentration of the cloud 29,the attenuation of the electromagnetic energy originating in source 10and propagated through guide 14 and cloud 29 may be varied.

The actual dimensions of the metallic wave guide and the length andflare of the electronic horn ultimately depend on whether a round orrectangular wave guide is employed and on the type of secondary focusingmeans incorporated. For purposes of illustration, a circular wave guidehaving an inner diameter of 1.15" and an electron horn flaring to 1.75",inner diameter, are suitable.

The parameters hereinabove mentioned are given by way of illustrationand not of limitation and this invention is not limited to theparticular dimensions given or to the particular application shown. Thisinvention resides in the providing of an electron cloud for deflecting,reflecting and/or attenuating in a controllable fashion electromagneticwaves, and in the provision of means for controlling the electron cloud,and should not be limited by the structure of any particular electrongun. Moreover, while it is not desired to be limited to any particularscientific theory for explaining the operation of this invention, it isbelieved that the thickness of the electron cloud required for completereflection is a function of the energy concentration to be reflected. Itis indicated in the classical treatises on electromagnetic theory thattotal reflection occurs from a cloud of electrons for a given frequencyand that the phenomenon is a surface one without any penetration.However, it is currently considered that reflection does not occur atthe cloud surface when the energy of the electromagnetic beam becomesgreat. Applying elementary mechanics to the motion of an electron underthe influence of the potential only at a 50 kw. 3 cm. wave, itis foundthat a cloud of 10 electrons per cubic centimeterwill be penetrated to adepth of 0.25 cm. before sufficient electron weight is encounteredtotally to reflect the wave potential. It is possible that laterinvestigations will reveal that the electrons oscillate in circularpaths due to the magnetic field of the wave, as well as in the linearpaths required by the potential of the wave. Advanced researches made ata later time may permit the provision of an electron cloud of lesserthickness than the one indicated above.

A certain gas pressure cannot be exceeded for a given energy withoutincurring the risk of auto-ionization. This pressure is a function ofthe molecular spacing and the maximum electronic oscillation under theinfluence of the electromagnetic wave. For 50 kw. waves this pressurelies well under 5 mm. of mercury. For low energy waves spontaneousionization is not to be feared, and any pressure is acceptable from thisstandpoint.

On the other hand the lower the pressure, the longer the free path, thegreater the electron velocity and the higher the cathode currentrequisite to establish the desired concentration. Argon has been foundto be the most satisfactory of the gases employed in practice. Thepresence of mercury is valuable in shortening the mean free path ofelectron travel. In practice, excellent results have been obtained withargon at a pressure in the neighborhood of 1 mm. with mercury added. Anelectron flow of 300 milliamperes with a potential gradient of 1.2 voltsper cm. has been obtained. An electron cloud set up in this manner issufficient to form the horn 29 of the nutator.

It will be seen that means have been disclosed herein for providingelectrical nutation of a stream of radiant energy without using anymechanically moving parts. Since the cathode ray beam comprises solelyelectrons and ions, its inertia is very small and the pattern ofnutation may be changed abruptly, thus avoiding the delays due toinertia in mechanical-type nutators heretofore employed. This featuresaves important seconds otherwise lost in combat operations during theshift from elliptic to circular nutation and thus decreases the dangerof losing the target at such time. Moreover. this nutator is exeremelyfast-acting and can be operated at a high nutation rate.

While the embodiment disclosed herein appears at present to thepreferred form of the present invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the spirit of the invention and it is,accordingly, intended that the appended claims cover also all suchchanges and modifications. The invention resides broadly in novelarrangements and processes for causing the-reflection and/or attenuationof an electromagnetic wave by an electron cloud. It will also be obviousto those skilled in the art that magnetic beam-deflecting members may besubstituted for the electrostatic beamdeflecting elements shown.

What is claimed is:

1. The process of deflecting a radiant energy beam which comprisesprojecting said beam through an opening extending through an electroncloud and controlling said cloud together within its opening to vary thedefiection of said beam.

2. In combination, means for producing a radiantenergy beam and meansfor producing a cloud of electrons having a passage extendingtherethrough, the lastnamed means being so positioned with respect tothe firstnamed means that said beam passes through said passage and issurrounded by the cloud.

3. In combination, means for producing a radiantenergy beam, means forproducing an apertured cloud of electrons, the last-named means being sopositioned with respect to the first-named means that said beam passesthrough an aperture in said cloud, and means for varying acharacteristic of said cloud, thereby to determine a characteristic ofsaid beam.

4. The combination in accordance with claim 3 and in which thelast-named means is for deflecting said cloud and the position of saidaperture, thereby to determine the direction of transmission of saidbeam.

5. In combination, cathode-ray tube means for producing a tubulardefiectable electron beam, and means for projecting electromagnetic waveenergy through said tubular portion of said beam.

6. The process of guiding high-frequency electromagnetic energy whichcomprises the steps of forming an ionized space charge as a conduit andintroducing the energy to be guided into one end of said conduit.

7. The process of guiding high frequency energy which comprises thesteps of producing in a low-pressure aeriform medium a tubularinertialess guide having a bore comprising electrons and ions andintroducing the energy to be guided into said guide, wherebysubstantially total internal reflection confines the high frequencyenergy within said bore of said guide, thereby to determine thedirection of transmission of said energy.

8. The process in accordance with claim 7 and in which said guide iselectrostatically deflected.

9. An electronic tube for providing a tubular cloud of electrons andions comprising an envelope, a wave guide having a portion extendinginto said envelope, and an electron gun structure surrounding saidportion.

10. In a radiant-energy transmission system a wave guide comprising asolid reflecting portion and a reflecting portion consisting solely ofan artificially produced electron cloud, said cloud constituting a tubewhich forms a continuation of the solid portion of the wave guide.

11. In a radiant-energy transmission system a wave guide comprising asolid reflecting portion and a reflecting portion consisting entirely ofa controllable electron cloud, of such shape and configuration that itconstitutes a continuation of the wave guide.

12. In a radiant-energy transmission system, a wave guide comprising asolid reflecting portion and a reflecting portion consisting wholly ofan artificially produced electron cloud, constituting a tubular waveguide portion forming an extension of the said solid portion of theguide and means for controlling a characteristic of said cloud, therebyto control a characteristic of the transmission of said radiant energy.

13. A radiant-energy confining arrangement comprising a rigid wave guideand means for producing an electron cloud in continuity with said waveguide, said cloud and said wave guide cooperating to confine saidenergy.

14. The process of guiding high frequency electromagnetic energy, whichconsists in producing a tubular field having a bore, comprisingelectrons and positive ions, in a low pressure gaseous medium,deflecting said tubular field by means of electric and/or magneticfields, and introducing the energy into the bore of said tubular field,whereby substantially total internal reflection will confine the highfrequency energy within said bore.

15. An electronic tube for providing a tubular field of ions andelectrons, said tube comprising a gas-tight en-,

velope, a wave guide extending through said wall of said envelope andhaving a portion projecting into the interior thereof and a set ofelectrodes, including, a cathode and control electrodes surrounding saidportion of said wave guide, said envelope having a suitable degree ofpartial vacuum therein.

16. The method of deflecting a radiant-energy beam which comprises thesteps of projecting a radiant-energy beam through a tubular stream ofelectrons, and deflecting said tubular stream of electrons to securedisplacement of the apparent source of said radiant-energy beam.

17. The method of deflecting a radiant-energy beam which comprisesforming a tubular'stream of electrons to guide a beam of radiant-energyfed to the center of said tubular electron stream, and deflecting saidtubular electron stream in any desired fashion and rate so as to causethe apparent source of said radiant-energy beam to be displaced in anydesired fashion.

18. In combination, a wave guide having a first passageway extendingtherethrough, and means for producing an electron cloud at one end ofsaid wave guide, said cloud having a second passageway extendingtherethrough, said second passageway being arranged to be an extensionof said first passageway in said wave guide, whereby electromagneticenergy can be propagated through said passageways of said wave guide andsaid electron cloud.

19. In combination, a wave guide having a first passageway extendingtherethrough, and cathode-ray tube means for producing a defiectableelectron beam, said beam having a second passageway extendingtherethrough, said second passageway being arranged so that it is acontinuation of said first passageway in said wave guide, wherebyelectromagnetic energy can be propagated through said passageways ofsaid wave guide and said electron beam.

References Cited in the file of this patent UNITED STATES PATENTS1,309,031 Hettinger July 8, 1919 1,687,792 Rave Oct. 16, 1928 2,047,930Linder July 14, 1936 2,064,469 Haefi Dec. 15, 1936 2,064,582 Wolfi Dec.15, 1936 2,085,406 Zworykin June 29, 1937 2,242,275 Varian May 20, 19412,300,052 Lindenblad Oct. 27, 1942 2,391,914 McElhannon Jan. 1, 1946FOREIGN PATENTS 555,325 Germany July 22, 1932

